When two antennas are near each other, coupling occurs between them. Such coupling can alter the directivity of the antennas thereby causing various problems in the operations of the host system. For example, in a radar system, detection of a target becomes very difficult if some of the transmitted electromagnetic waves directly leak into the receiving system. Hence, it is necessary to suppress occurrence of coupling between a transmitting antenna and a receiving antenna.
A conventional approach to suppress the amount of coupling between the antennas is to arrange a choke, which is in the form of a groove, between the antennas. Based on a result of a study that indicated that it is preferable that the impedance of the choke be infinite, in the conventional approach the groove with the depth of 0.25λ is employed, wherein λ is the wavelength of a carrier wave (refer to Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-Open No. H10-163737